/**
	 * Clear local wikinav cache when local version of global menu
	 * is modified using WikiFactory
	 *
	 * @param string $cv_name WF variable name
	 * @param int $city_id wiki ID
	 * @param mixed $value new variable value
	 * @return bool return true
	 */
	public static function onWikiFactoryChanged($cv_name , $city_id, $value) {
		global $wgMemc;

		if ($cv_name == WikiNavigationService::WIKIA_GLOBAL_VARIABLE) {
			$service = new NavigationService();
			$memcKey = $service->getMemcKey(WikiNavigationService::WIKIA_GLOBAL_VARIABLE, $city_id);

			wfDebug(__METHOD__ . ": purging the cache for wiki #{$city_id}\n");

			$wgMemc->delete($memcKey);
		}

		return true;
	}