Is it possible to kasher a pot that has areas that are hard to clean, for example the rim? Is there anything one can do to these areas if they can't be completely cleaned out that will allow the pot to be kashered?
The Shulchan Aruch HaRav writes:
One cannot do Hagala on a knife or any other vessel needing Hagala that has a hole or a crack that's not cleanable, as we're concerned that it may be pieces of visible Chometz there, and Hagala doesn't remove visible chometz. Therefore, one has to place burning coals on the crack until the knife gets hot enough that the other side of it will be Yad Soledes bo, as the chametz will definitely be burned up.
The world, however, is accustomed to put the coals long enough that straw touching the other side of the knife will start burning.
Then one does regular Hagalah.