Best Way to Clean Wallpaper Safely?

The plumber repaired my toilet OK, but he left a lot of grime and stains on the wallpaper behind the toilet in the bathroom, which don't seem to come off easily.
What's the best way to clean wallpaper? Too much scrubbing could damage the finish, and I don't want anything that will damage the color or the wallpaper paste.
-- Steven L.
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