After a bit of thought, I realized that there was a single switch box
in the kitchen that contained lights from both circuits...
one switch (a 3-way) controls the light in the foyer and the rest
control kitchen lights. That seemed like a likely spot
to start looking so I pulled it open. I discovered that all of the
neutrals in the box were tied together, crossing the two
circuits together. I pulled the incoming and outgoing neutrals for
the foyer light out and tied them together separately
and the problem is fixed.

Thanks to all for the advice.