I keep a pile of small pieces of scratch paper (DIN A-8 and A-9 in size) both at home and at work (I'd keep them in the car too, should I own one) where I write down whatever I need to do when I go to another location (room inside the building or even other places outside the building). When I move to another location, I take the relevant tiny notes with me, do the task and through away the note.

I started doing that because I was so frustrated always having that doorway effect you mention. Going back to the previous location often triggered the idea again, though not always, but in any case, it's a waste of time. The time and effort that takes writing those tiny notes pays (for me at least) without any doubt.