Honestly, I think that wiping cache is overrated and it *shouldn't* improve performance - it should have a short-term decrease as the cache rebuilds, and then the new cache will basically be what the old cache was. I still think that people who report performance improvements are suffering a bit of placebo effect.
It is possible that if cache gets corrupted that wiping cache will help, though I think that is a very rare occurrence.
Still, the steps are somewhat easy, and Motorola has them right on their site:
Clear Cache Partition