code: public void clear (final Name username)
      {
          // if we're holding this username for a session observer, postpone until after the current
          // dispatch finishes
          if (_holds.contains(username)) {
              _holds.remove(username);
              _omgr.postRunnable(new Runnable () {
                  public void run () {
                      clear(username);
                  }
              });
              return;
          }
  
          // Log.info("Clearing history for " + username + ".");
          _histories.remove(username);
      }
docs: Clears the chat history for the specified user.