Google's Vice President, Benjamin Sloss, who has 599XX Evoluzione and a FXX K recently cleared the rumor on Instagram, saying that XX owners can keep their cars anywhere they like. He also said that owners can enter their vehicle's into track days which haven't been organised by Ferrari.
Road & Track, an American publication then went on further to clarify things by contacting Ferrari. The below is what Ferrari replied.
“The majority of the cars are stored in Maranello in the Corse Clienti department, but customers are free to have them at home. It is mandatory, however, to have a full review of the car by the Ferrari crew team before the car hits the track in any event or private testing session. Anytime the car is taken to the track, for an official Ferrari event or personal test session, there is always a mechanic and technician. He'll do the full check up when the car arrives at that said track.”
Guess the old rumor isn't true after all!