code: func (rsrbds *repositoryScopedRedisBlobDescriptorService) Clear(ctx context.Context, dgst digest.Digest) error {
  	if err := dgst.Validate(); err != nil {
  		return err
  	}
  
  	conn := rsrbds.upstream.pool.Get()
  	defer conn.Close()
  
  	// Check membership to repository first
  	member, err := redis.Bool(conn.Do("SISMEMBER", rsrbds.repositoryBlobSetKey(rsrbds.repo), dgst))
  	if err != nil {
  		return err
  	}
  
  	if !member {
  		return distribution.ErrBlobUnknown
  	}
  
  	return rsrbds.upstream.Clear(ctx, dgst)
  }
docs: // Clear removes the descriptor from the cache and forwards to the upstream descriptor store