code: function () {
              this.$pageCache = {};
  
              for (var key in this.$filterCache) {
                  if (this.$filterCache.hasOwnProperty(key)) {
                      this.$filterCache[key].invalidatePageCache();
                  }
              }
  
              for (key in this.$sortCache) {
                  if (this.$sortCache.hasOwnProperty(key)) {
                      this.$sortCache[key].invalidatePageCache();
                  }
              }
  
              this.set('$itemsCount', NaN, {silent: true});
              this.reset([]);
          }
docs: This method invalidates the page cache of the collection.
  It also clears all page caches of query collections, that have this collection has root collection.
  After the invalidation the $itemsCount is set to NaN and a reset is done. So all listeners are informed of the change.
  
  You should call this method after removing or adding some item to the collection.