My pekes love to relax next to the wall, and wipe their faces on it.
An easy way to clean these stains are white vinegar and hot water.
I mix 2/3 of  white vinegar to 1/3 of hot water.
Pour some on a soft cloth and gently white the wall, the stains should go right away. If stains are reluctant I use a soft brush.
I use a dry cloth to wipe off any liquid left.

Before

After, it looks much cleaner