|Urushiol is a "sticky" oil and yes it does seem to easily get transfered to clothing, furniture, tools, fur, etc. That secondary source is how many of us end up being exposed even though we weren't in direct contact with poison ivy/ oak / sumac.
That said - urushiol is an oil and as such can be washed off of items. If you can remove any covers of the couch such as couch cushion covers, you can toss those in the washing machine and use a good detergent. There is an article here on the site about how soap works: http://www.poisonivy.us/view/soap.html . This explains how a good detergent along with water will remove the urushiol oil.
For fixed items like the couch -- I would probably use a rug steam cleaner. The ones I've seen have an upholstery attachment. This would allow you to use a detergent and then clean up with water. That's the key is to get the detergent in to attach to the urushiol and then use copious amounts of water to flush it out. The cleaner would suck up the water / detergent mix.
Hope this helps.