Run Code on Drupal Cache Clear

Drupal 7's hook_flush_caches() allows you to register a cache table name to be truncated like this:

function hook_flush_caches() {
  return array('cache_example');
}

If you want to run custom logic, you can register a shutdown function in hook_flush_caches() to fire code immediately after this function completes.

<?php
/**
 * Runs a cache clearing routine other than just truncating cache table.
 */
function _MYMODULE_after_cache_clear() {
  // Add your post cache clear logic here.
}


/**
 * This hook allows you to add the name of a cache table to be truncated
 * whenever the caches are flushed. By registering a shutdown function here,
 * we can fire an event immediately after hook_flush_caches() completes.
 */
function MYMODULE_flush_caches() {
  register_shutdown_function('_MYMODULE_set_cleared');
  return array();
}