What we did with Java (J/SAFE) was to add explicit methods to zero out sensitive info. It was a bit of a PITA because Java's never had consistent semantics about when final(ize,ly) methods were called. Later we added code to track which objects were allocated, but no longer needed, which also wasn't much fun.

Back in the Oak days Sun asked us (I was at RSADSI at the time) to review the language spec for security implications. Our big request was to add the "secure" storage specifier for data. The idea being a variable, const, whatever that was marked "secure" would be guaranteed not to be swapped out to disk (or one of a number of other system specific behaviors). But it was hard to find a concrete behavior that would work for all platforms they were targeting (mostly smaller systems at the time.)

My coworker Bob Baldwin had an existing relationship with Bill Joy and James Gosling (I'm assuming as part of the MIT mafia) so he led the meetings. Joy's response (or maybe Goslings, can't remember anymore) was "Language extension requests should be made on a kidney. Preferably a human kidney. Preferably yours. That way you'll think long and hard about it and you sure as hell won't submit 2."