I think you mean the recess in the breech not the bolt. There is not much need to clean the groove where the extractor spring and plunger sit (other than spraying them out once in a while) since the extractor tension is via a spring and there would have to be quite a build up of gunk to affect the spring. The recess for the extractor in the breech should be cleaned every time you clean the breech area.
I also use dental picks to get to tight places but...use caution since dental picks are made from a 400+ grade stainless and are much harder than "gun stainless". They can scratch and gouge gun metal.