function addListener(scope, hashKey) {
        var id = scope.$id;
        if(isUndefined($$listeners[id])) {
          scope.$on('$destroy', removeCache);
          $$listeners[id] = [];
        }
        return $$listeners[id].push(hashKey);
      }
@description
Store hashKeys in $$listeners container
on scope.$destroy, remove them all(bind an event).
@param scope
@param hashKey
@returns {*}