Okay, the reason I wanted instructions for rebuilding my Subsonic database was I was seeing a lot of indications of a corrupted database and I couldn't find any clear instructions for rebuilding.
There were many signs that my dBase was corrupted but I ended up going to my C drive, finding the "db" folder under Subsonic (C:/subsonic) and moving the files within that folder elsewhere in case I needed to restore them.
I then went to the web interface via
http://localhost:4040 (4040 or whatever port you have set for your access). My original login credentials still worked.
Anyway, once there, I went into Settings-->Media folders. The media folders I had had Subsonic pointing to were now gone so I re-entered those and then did the "Scan media folders now" operation. The scanning countdown showed the scanning was working, but things still didn't behave correctly. Note: Also gone were all Users, by the way.
Kept fiddling around trying different things. Eventually, and at wits' end, I tried deleting and then re-entering the media folders again (exactly as they had been entered before) and, voila! All my music suddenly showed up, without even rescanning (??)
So, in the end, I don't know if any of this will be the solution for anyone else, but somehow it was for me.
Good luck!
P.S. I still haven't seen clear instructions for rebuilding the dBase, but perhaps my haphazard approach (clearing the Subsonic db folder on my C drive of any files and then rescanning from the web interface) is the way (?).