code: function() {
          for (var key in this.layerCache) {
              delete this.layerCache[key];
          }
          for (var key in this.wfsCache) {
              delete this.wfsCache[key];
          }
          OpenLayers.Control.prototype.destroy.apply(this, arguments);
      }
docs: APIMethod: destroy
  Take care of things that are not handled in superclass.