diff --git a/core/lib/Drupal/Core/Cache/CacheTagInterface.php b/core/lib/Drupal/Core/Cache/CacheTagInterface.php
index fd09b70..773f101 100644
--- a/core/lib/Drupal/Core/Cache/CacheTagInterface.php
+++ b/core/lib/Drupal/Core/Cache/CacheTagInterface.php
@@ -34,8 +34,25 @@ public function deleteTags(array $tags);
    */
   public function invalidateTags(array $tags);
 
+  /**
+   * @param array $tags
+   *   Associative array of tags.
+   * @return array
+   *   Array with two items (invalidations, deletions) providing sum of all
+   *   invalidations/deletions over all provided tags.
+   */
   public function checksumTags(array $tags);
 
+  /**
+   * Prepares cache item before it is returned from cache backend interface.
+   *
+   * $item->deleted should be set to TRUE if item was deleted via tags and
+   * $item->valid should be set to FALSE if item was invalidated.
+   */
   public function prepareGet(&$item);
 
+  /**
+   * Clears cache tag service internal caches.
+   */
+  public function clearCache();
 }
diff --git a/core/lib/Drupal/Core/Cache/DatabaseTag.php b/core/lib/Drupal/Core/Cache/DatabaseTag.php
index 10f6a9e..4d05ef9 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseTag.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseTag.php
@@ -144,4 +144,10 @@ protected function catchException(\Exception $e, $table_name = NULL) {
     }
   }
 
+  /**
+   * {@inheritdoc}.
+   */
+  public function clearCache() {
+    $this->tagCache = array();
+  }
 }
diff --git a/core/lib/Drupal/Core/Cache/MemoryBackend.php b/core/lib/Drupal/Core/Cache/MemoryBackend.php
index 261712b..9d6596a 100644
--- a/core/lib/Drupal/Core/Cache/MemoryBackend.php
+++ b/core/lib/Drupal/Core/Cache/MemoryBackend.php
@@ -93,7 +93,7 @@ protected function prepareItem($cache, $allow_invalid) {
     // Check expire time.
     $cache->valid = $time_valid = $cache->expire == Cache::PERMANENT || $cache->expire >= REQUEST_TIME;
 
-    $this->cacheTag->prepareGet($item);
+    $this->cacheTag->prepareGet($cache);
     if ($cache->deleted) {
       $this->delete($cache->cid);
       return FALSE;
diff --git a/core/lib/Drupal/Core/Cache/MemoryTag.php b/core/lib/Drupal/Core/Cache/MemoryTag.php
index 616732c..b82248b 100644
--- a/core/lib/Drupal/Core/Cache/MemoryTag.php
+++ b/core/lib/Drupal/Core/Cache/MemoryTag.php
@@ -94,4 +94,11 @@ public function prepareGet(&$item) {
       $item->valid = FALSE;
     }
   }
+
+  /**
+   * {@inheritdoc}.
+   */
+  public function clearCache() {
+    // Nothing to be done here.
+  }
 }
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
index c3fc74e..04064ce 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
@@ -142,7 +142,7 @@ function testStringTranslation() {
 
     // Reset the tag cache on the tester side in order to pick up the call to
     // Cache::deleteTags() on the tested side.
-    drupal_static_reset('Drupal\Core\Cache\CacheBackendInterface::tagCache');
+    $this->container->get('cache.tag.database')->clearCache();
 
     $this->assertTrue($name != $translation && t($name, array(), array('langcode' => $langcode)) == $translation, 't() works for non-English.');
     // Refresh the locale() cache to get fresh data from t() below. We are in
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index 92b161f..1dcb454 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -190,6 +190,7 @@ public function containerBuild(ContainerBuilder $container) {
 
     $container->register('lock', 'Drupal\Core\Lock\NullLockBackend');
     $this->settingsSet('cache', array('default' => 'cache.backend.memory'));
+    $this->settingsSet('cache_tag_service', 'cache.tag.memory');
 
     $container
       ->register('config.storage', 'Drupal\Core\Config\FileStorage')
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 3917ffa..334a4a0 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -775,6 +775,7 @@ protected function setUp() {
     // Execute the non-interactive installer.
     require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
     $this->settingsSet('cache', array('default' => 'cache.backend.memory'));
+    $this->settingsSet('cache_tag_service', 'cache.tag.memory');
     $parameters = $this->installParameters();
     install_drupal($parameters);
 
@@ -1004,7 +1005,7 @@ protected function resetAll() {
    */
   protected function refreshVariables() {
     // Clear the tag cache.
-    drupal_static_reset('Drupal\Core\Cache\CacheBackendInterface::tagCache');
+    $this->container->get('cache.tag.database')->clearCache();
 
     \Drupal::service('config.factory')->reset();
     \Drupal::state()->resetCache();