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  $mode   The mode for cleaning cache [group|notgroup]
 *
 * @return  boolean
 *
 * @since   3.4
 */
public function clean($group, $mode = null)
{
    if (static::isConnected() == false) {
        return false;
    }
    $allKeys = static::$_redis->keys('*');
    if ($allKeys === false) {
        $allKeys = array();
    }
    $secret = $this->_hash;
    foreach ($allKeys as $key) {
        if (strpos($key, $secret . '-cache-' . $group . '-') === 0 && $mode === 'group') {
            static::$_redis->del($key);
        }
        if (strpos($key, $secret . '-cache-' . $group . '-') !== 0 && $mode !== 'group') {
            static::$_redis->del($key);
        }
    }
    return true;
}