expire_cache_derivative() gets absolute URL for $path_alias when domain-based language negotiation is on

In expire_cache_derivative(), when domain-based language negotiation is used, the resulting URL is absolute regardless, as a side-effect of language_url_rewrite():

$path_alias = url($path, array('absolute' => FALSE));

Recommend getting the path alias directly, with

$path_alias = drupal_get_path_alias($path);