I could think of 5 different answers during the first ten seconds, so obviously you need to narrow the question down a bit. Do you mean project scope? variable declaration scope? scope of different roles such as programmer, designer, etc. in such projects? The "scope creep" effect for such projects? The accepted scope of an "incremental change" ... personally I question whether extreme programming is a proper methodology as opposed to being what happens when IT people are put under pressure to deliver without ever being given the chance to "clean the kitchen" (I realise I suffer from it frequently!!)
^M Free your mind!