Nobody likes frames anymore* but...
(if you'd just like them to restart at your index page)
when a page loads use javascript to detect an attribute (the title is simple) of the 'top' document that you know is the frameset. If it's not what you expect then relocate the whole lot to the frameset page.

otherwise:
pretty awkward. Depending on browser/ethics/time/security/bothered/effort

- try and find out what's calling your page before sending it (then DO/DON'T)

- on load/reload the top document you might be able to access history (previous locations) and then extract the last document url (if appropriate) and load it to the appropriate frame once everything else has loaded.

- leave a cookie, check a cookie, read a cookie, use a cookie

- call/create your frameset via cgi with variables but... that's just a very hard way of doing what other stuff does easily.

I've always liked (sensible) frames. It allowed you to load data at the start of a session (keep it) and use it to call more content without resorting to 'say that again?' & 'once more for luck' & 'oh, I say, have you seen this picture before?'

*Give it a little while and somebody'll reinvent a way of including bits of pages in other pages to make things smooth, quick and reduce demands on bandwidth... ahem!

Oh Uncle Dog... we don't like javascript! we love PHP, rss, mxm, pqr, sqvp, rsvp