Go to a pet supply store and buy a bottle of "Nature's Miracle" odor and stain remover."Nature's Miracle" is an enzymatic cleaner designed to take out organic stains.
Get a sponge and use it to dab the product onto the stained area using a gentle dabbing motion, then blot up the area with a clean towel. Repeat the procedure until the stain is gone and then allow the cloth to dry over a 24 hr period.
Woolite will also work well, just make sure you dilute it sufficiently with distilled water to avoid mineral stains after the cloth dries.