public void TagRemoved(string tag, IEnumerable <string> keys)
 {
     foreach (var key in keys)
     {
         _dynamicCache.RemoveAsync(key);
     }
 }
 public Task TagRemovedAsync(string tag, IEnumerable <string> keys)
 {
     return(Task.WhenAll(keys.Select(key => _dynamicCache.RemoveAsync(key))));
 }