code: @SuppressWarnings("unused") // called through reflection by RequestServer
    public FramesV3 deleteAll(int version, FramesV3 frames) {
      final Key[] keys = KeySnapshot.globalKeysOfClass(Frame.class);
  
      ArrayList<String> missing = new ArrayList<>();
      Futures fs = new Futures();
      for (Key key : keys) {
        try {
          getFromDKV("(none)", key).delete(null, fs);
        } catch (IllegalArgumentException iae) {
          missing.add(key.toString());
        }
      }
      fs.blockForPending();
      if( missing.size() != 0 ) throw new H2OKeysNotFoundArgumentException("(none)", missing.toArray(new String[missing.size()]));
      return frames;
    }
docs: Remove ALL an unlocked frames.  Throws IAE for all deletes that failed
  (perhaps because the Frames were locked & in-use).