Need a little help on the melee group vs the first boss.

Divine Reckoning : is this the dot that I have to cleanse ? Or it heals the boss back to full ? or It heals the boss anyway regardless if I cleanse it or not.

I am running with rets can't really dispel anything. If cleanse is required, then I have to switch to a holy paladin. Also I was thinking, what happen if I drag him down to the stairs? So I am closer to the switches. OR I have to fight him on 2nd floor.