Change property of the location of the actor?

So I made an NPC that wanders around “cleaning” the rooms. The rooms are indicated as clean or dirty by a property: clean or dirty.
Since the NPC wouldn’t necessarily be in the room with the player when it cleans, how would I do this?

You already have the right syntax in your topic title. The room in which X is can be referred to as “the location of X”. So a phrase like “now the location of X is clean” should do the trick.

Okay, I was having trouble when the player orders the NPC to do it, and wasn’t sure where things were buggering up.