Method clean

/**
 * Clean cache for a group given a mode.
 *
 * group mode    : cleans all cache in the group
 * notgroup mode : cleans all cache not in the group
 *
 * @param   string  $group  The cache data group
 * @param   string  $mode   The mode for cleaning cache [group|notgroup]
 *
 * @return  boolean
 *
 * @since   3.5
 */
public function clean($group, $mode = null)
{
    $allinfo = apcu_cache_info();
    $keys = $allinfo['cache_list'];
    $secret = $this->_hash;
    foreach ($keys as $key) {
        if (isset($key['info'])) {
            // The internal key name changed with APCu 4.0.7 from key to info
            $internalKey = $key['info'];
        } elseif (isset($key['entry_name'])) {
            // Some APCu modules changed the internal key name from key to entry_name
            $internalKey = $key['entry_name'];
        } else {
            // A fall back for the old internal key name
            $internalKey = $key['key'];
        }
        if (strpos($internalKey, $secret . '-cache-' . $group . '-') === 0 xor $mode !== 'group') {
            apcu_delete($internalKey);
        }
    }
    return true;
}