You need a VAG-COM cable to reset most codes on these cars as well as to do many other procedures including resetting certain convenience items such as chimes, window and lock behavior.
Ross Tech sells them as well as the software. I purchased one of the ebay knock off cables and I am using the free software from the ross tech site.
This cable is good to have if you do any of your own work. Great for checking codes and in many cases you have to have it to complete procedures (throttle body adaptation, transmission fluid checking).