code: public synchronized void schedulePurge() {
  		assert acquired || workbenchEntry == null : acquired + " " + workbenchEntry;
  		frontier.schemeAuthority2Count.put(schemeAuthority, Integer.MAX_VALUE);
  		nextFetch = Long.MAX_VALUE;
  		clear();
  	}
docs: Disables permanently this visit state and schedules its purge
  by setting the {@linkplain Frontier#schemeAuthority2Count count} associated
  with its {@link #schemeAuthority} to {@link Integer#MAX_VALUE}, {@linkplain #clear() clearing} the internal queue and
  setting {@link #nextFetch} to {@link Long#MAX_VALUE}.