public function purgeByCacheKey($cacheKey)
    {
        // initialize log
        $log = new DebugLog();
        $log->addMessage('State', 'Purge by cache key');

        // remove the key from index
        $this->indexStorage->deleteEntryByKey($cacheKey);

        // purges from cache storage
        return $this->cacheStorage->purge($cacheKey);
    }