Tibouchina is definitely not hardy, and will have to be overwintered indoors. The trick is where and what conditions you can offer it, if there is no greenhouse. I have not tried, but generally try to keep non-hardy things barely growing (a cool bright room, not a lot of water and no food). A potted specimen won’t reach its in-the-ground potential, and besides, you will probably be doing some pruning as I expect it will hate you for bringing it indoors. I wish I had more specifics, but have seen very little of authority on this topic to share.