public function getSiteHashForDomain($domain)
    {
        static $siteHashes = [];
        if (isset($siteHashes[$domain])) {
            return $siteHashes[$domain];
        }

        $siteHashes[$domain] = sha1($domain . $GLOBALS['TYPO3_CONF_VARS']['SYS']['encryptionKey'] . 'tx_solr');
        return $siteHashes[$domain];
    }