I cleaned it very thoroughly as follows.

-Remove EGR valve from exhaust manifold, clean inside gently to remove some tar
-Soaked the tube connecting manifold and EGR in carb cleaner to remove all tar
-Removed EGR from air intake and ran a tube from it to under the car into a bottle to collect crap, soaked the EGR tube in cleaner (with a stopper in the outlet tube to let it really soak) multiple times for a whole day using a speedo cable and some air. By the time I was done any cleaner in the exhaust side immediately ran out the intake side
-Cleaned the little port in the intake thoroughly
-Put in a new EGR gasket

I checked the EGR valve while I had it off the car and it seemed to be functioning properly