Most washable wallcoverings can be scrubbed clean with a sponge and nonabrasive cleanser. Try that with a nonwashable wallcovering, and you'll ruin the surface. A little-known secret: Most greasy, grimy stains and spots can be drawn out of nonwashable wallcoverings with a standard electric clothes iron. Place both layers of a regular brown grocery bag right over the stain. Press the paper with a warm iron — no steam — for a minute or two. The paper will absorb the heated grease. If necessary, repeat the process with clean paper until the stain lifts out.