Really? This is the first that came to mind for me. The only one that might "outrank" it in my mind is the Pantheon, but I wouldn't think anyone would refer to that as "Italy's famous dome", they'd just say "the Pantheon".

Plus the original title in the URL specifically calls it "Brunelleschi's dome", which even if you don't know/remember Brunelleschi, does rule out the Pantheon just from the name.