I recently moved in to a new office that was freshly painted and discovered that there were whiteboard walls for me to use. I really like whiteboards, they are brilliant for drawing on and clearly communicating ideas, and the bigger they are the better. I was drawing on the wall and when I got to the corner I noticed that the gloss finish ended and was immediately next to a matt one. I came very close to drawing on a wall that wasn't a whiteboard because it's all white!
Paint the walls that aren't whiteboards a different colour, for example light grey. Or if you're very attached to having white walls everywhere then provide a marker (painted, stuck on, etc.) to indicate where the section of wall you can write on ends.