I can't answer your question since I don't spend time in CoD, but if there is no other reward besides the "Grummus Flag" you may want to take a look into just killing Grummus. I boxed him about a month ago and it was extremely easy. I am a moderately geared monk...was about 15k/2.4k cleric buffed and used a haste potion. I used cleric for cure and only used HoT's. Was very easy.
At the very least he can be killed with less than 1 group easy as long as you have a cleric or shammy there for cures.
Just another option.