Archiving means moving from one location to another for long term storage (possibly aggregation, possibly other stuff, that really depends on your business needs, I can't define this for you). Purging means removing it, period. Archiving involves both inserting/updating (possibly even deleting, again, your business needs define this) to the new location, and deleting from the old location. So purging is actually a part of archiving.

As to a generic method, there sort of isn't one. You have to understand what your business wants out of this process, what all the requirements are. Those requirements will drive your decisions around building out the process.