It just so happens that I am wrestling with that exact same problem myself tonight.
I noticed that if I take away the www. from the url, adsense generates a new batch of ads that are relevant to the pages content, but that doesn't solve the problem. If you go back to the www. page, the same irrelevant ads remain.
I've tried clearing my cache and a number of other techniques that I though would work, but to no avail...
