I would try an enzyme cleaner such as Nature's Miracle first. They have a formula made specifically for cats. I find it works better than their regular formula. Make sure to REALLY saturate the area, and let it SIT until it dries on its own. Many people use too little, blot it up, or dry it up, and it simply is not as effective that way.
However, I have had a few instances where the enzyme cleaner didn't work after multiple uses, and I have found that cleaning with oxygen bleach (or a higher concentration of peroxide, like you could buy in a beauty supply store) was what finally cleared the scent. If you buy powdered oxygen bleach, you can make a paste out of it. Just make sure that you do not let the animals ingest it.