safeUnloadCache(cache) {
           if (cache && !cache._destroyed && cache.getTileCount() < 1) {
               for (let i in this._zombiesLoaded) {
                   const c = this._zombiesLoaded[i];
                   if (c === cache) {
                       delete this._zombiesLoaded[i];
                       c.destroy();
                       return;
                   }
               }
               $.console.error("Attempt to delete an orphan cache that is not in zombie list: this could be a bug!", cache);
               cache.destroy();
           }
        }
Delete cache safely from the system if it is not needed
@param {OpenSeadragon.CacheRecord} cache