diff --git a/varnish.admin.inc b/varnish.admin.inc
index 515057a..99505d7 100644
--- a/varnish.admin.inc
+++ b/varnish.admin.inc
@@ -114,6 +114,25 @@ function varnish_admin_settings_form() {
     ),
   );
 
+  // Allow users to specify specific domains to use.
+  $form['varnish_hosts'] = array(
+    '#type' => 'fieldset',
+    '#title' => t('Hosts'),
+    '#collapsible' => TRUE,
+  );
+  $form['varnish_hosts']['varnish_hosts_use_baseurl'] = array(
+    '#type' => 'checkbox',
+    '#title' => t('Always include the current host'),
+    '#description' => t('Allow the Varnish module to always include the current host (parsed from the $base_url of the current request). Uncheck this to strictly control the hosts to be used.'),
+    '#default_value' => variable_get('varnish_hosts_use_baseurl', TRUE),
+  );
+  $form['varnish_hosts']['varnish_hosts_list'] = array(
+    '#type' => 'textarea',
+    '#title' => t('Hosts list'),
+    '#description' => t('Specify each host (domain) that is associated with this site. One host per line.'),
+    '#default_value' => variable_get('varnish_hosts_list', ''),
+  );
+
   // Check status.
   $form['varnish_stats'] = array(
     '#type' => 'item',
diff --git a/varnish.cache.inc b/varnish.cache.inc
index 3d30bf3..6b5a404 100644
--- a/varnish.cache.inc
+++ b/varnish.cache.inc
@@ -71,10 +71,12 @@ public function clear($cid = NULL, $wildcard = FALSE) {
           varnish_purge_all_pages();
         }
         else {
-          $host = _varnish_get_host();
           $base = base_path();
           $purge = $cid . '(.*)';
-          varnish_purge($host, '^' . $base . $purge . '$');
+          // Purge for all selected hosts.
+          foreach (_varnish_get_hosts() as $host) {
+            varnish_purge($host, '^' . $base . $purge . '$');
+          }
         }
       }
       elseif (is_array($cid)) {
diff --git a/varnish.module b/varnish.module
index 925ca06..dfa017d 100644
--- a/varnish.module
+++ b/varnish.module
@@ -126,8 +126,9 @@ function varnish_expire_cache($paths, $wildcards = array()) {
     }
   }
   else {
-    $host = _varnish_get_host();
-    varnish_purge_paths($host, $paths);
+    foreach (_varnish_get_hosts() as $host) {
+      varnish_purge_paths($host, $paths);
+    }
   }
 }
 
@@ -136,8 +137,9 @@ function varnish_expire_cache($paths, $wildcards = array()) {
  */
 function varnish_purge_all_pages() {
   $path = base_path();
-  $host = _varnish_get_host();
-  varnish_purge($host, $path);
+  foreach (_varnish_get_hosts() as $host) {
+    varnish_purge($host, $path);
+  }
 }
 
 /**
@@ -312,6 +314,30 @@ function _varnish_get_host() {
   return $parts['host'];
 }
 
+/**
+ * Helper function to get all hosts associated with this site. Invokes
+ * hook_varnish_hosts_alter() to fetch the list.
+ */
+function _varnish_get_hosts() {
+  $hosts = array();
+
+  // Include the host from the global $base_url, unless disabled.
+  if (variable_get('varnish_hosts_use_baseurl', TRUE)) {
+    $hosts[] = _varnish_get_host();
+  }
+
+  // Include additional hosts specified in the settings.
+  if ($hosts_list = variable_get('varnish_hosts_list', '')) {
+    foreach (explode("\n", trim($hosts_list)) as $host) {
+      $hosts[] = trim($host);
+    }
+  }
+
+  // Allow the varnish_hosts array to be altered.
+  drupal_alter('varnish_hosts', $hosts);
+
+  return array_unique($hosts);
+}
 
 /**
  * Helper function that sends commands to Varnish.