_clearCaches() {
    // clear all tiddler-caches below this path
    utils
      .getMatches(`[prefix[${this.getRoot()}]]`)
      .forEach(tRef => { $tw.wiki.clearCache(tRef); });
  }
This will clear all cached tiddlers related to this view.

@private
@return {boolean} true if the cache was dirty, false if cache was up-to-date and did