I throw mine in the washer with a special detergent. I also have a sheepskin saddlepad which gets really dirty, same thing. For drying I put mine on these laundry-stands. They come out absolutely beautiful. You can put 1/2 cup of vinegar in the last rinse, that softens the leather a bit.

Have a look at http://www.sheepskin.org.uk for information on how to clean your sheepskin rug. I think the general consensus is that the washing machine can be used but just make sure you clean it on its own. The site is more detailed than I!

Here is a link that might be useful: Sheepskin cleaning

What kind of soap would you use? Woolite?