As VR said, the villa — which was reproduced full-scale as the Getty Museum out in California — is believed to have belonged to Lucius Calpurnius Piso Caesonius. There has been speculation in recent years that there is at least one other storey to the house, and that the library itself may be continued there. It’s probably a pipe dream.
Given the vandalism done to scroll after scroll by the various parties involved, I’d just as soon have CAT-scanning to read them while still rolled up, before anyone puts another spade to the Earth, as it were.
http://www.getty.edu/museum/programs/lectures/roman_villas_lecture.html
http://en.wikipedia.org/wiki/Villa_of_the_Papyri
Knew it started with a P. Piso instead of Pliny.