    private synchronized void purgeOldMessagesFromMessagesToIgnore(int thisTurn) {
        List<String> keysToRemove = new ArrayList<String>();
        for (Entry<String, Integer> entry : messagesToIgnore.entrySet()) {
            if (entry.getValue().intValue() < thisTurn - 1) {
                if (logger.isLoggable(Level.FINER)) {
                    logger.finer("Removing old model message with key " + entry.getKey() + " from ignored messages.");
                }
                keysToRemove.add(entry.getKey());
