Had a similar experience this fall with my 2004 XC70-- 6" of the bottom of the driver's side front coil broke off! I know this is not an uncommon failure for the P2 XC70s, see volvoxc.com forums for lots of examples. You are lucky it broke in the garage-- others have described the coil fragments slashing tires...

I replaced both front coils along with the spring seats and sway bar end links, which can be a bear to get off in the rust belt. If I had it to do again, I would get Sachs quick struts (they were out of stock everywhere when I needed them). My XC70 only had about 100K mi on it, but one strut was already a bit weak, the bump stops were toast on both sides and the strut bearings didn't exactly look new anymore. For $250 per side, I would have had everything new again. It would have saved me a bunch of time messing around with spring compressors too...

Good luck!