private function purgeExpiredRoutes()
    {
        $expireTag = '';
        foreach ($this->routeProviders as $routeProvider) {
            /* @var $routeProvider UrlProviderInterface */
            $expireTag .= $routeProvider->getExpirationTag();
        }

        $value = md5($expireTag);

        $urlNodesCacheItem = $this->cachePool->getItem('splashExpireTag');

        if ($urlNodesCacheItem->isHit() && $urlNodesCacheItem->get() === $value) {
            return;
        }

        $this->purgeUrlsCache();

        $urlNodesCacheItem->set($value);
        $this->cachePool->save($urlNodesCacheItem);
    }