code: private void clearBeatGrids(DeviceAnnouncement announcement) {
          final int player = announcement.getNumber();
          // Iterate over a copy to avoid concurrent modification issues
          for (DeckReference deck : new HashSet<DeckReference>(hotCache.keySet())) {
              if (deck.player == player) {
                  hotCache.remove(deck);
                  if (deck.hotCue == 0) {
                      deliverBeatGridUpdate(player, null);  // Inform listeners the beat grid is gone.
                  }
              }
          }
      }
docs: We have received notification that a device is no longer on the network, so clear out all its beat grids.
  
  @param announcement the packet which reported the device’s disappearance