Hi,
The sensible answer would be to redirect, via a 301 perm reidrection, each old URL to the new most relevant new URL.
E.G. https://domain.com -> 301 redirect -> http://domain.com
This can be accomplished a number of ways depending on how your site is set up, what (if any) CMS you use along with whatever server and operating system you use.
It can be a royal PITA to map all the old URLs to new ones, but it will deliver the goal you want – specifically to remove old URLs from Google’s database but also to pass over any ranking opportunities on the new URL.
If you REALLY don’t want to pass any link love along to the new pages and just want to delete the old pages / subdomains, then as long as they are not there and you serve a 404 error message then http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=64033 is some wise reading material.