A switch gives every device its own private, collision-free wire. It still has to flood a broadcast frame out every other port on the same VLAN — those are two completely different jobs, and only one of them is solved by switching.
"Domain" shows up twice in networking vocabulary, describing two boundaries that used to line up almost perfectly on old hub-based networks and now almost never do. A collision domain is the set of devices whose transmissions can physically collide with each other on a shared medium — a real electrical event that shared-media Ethernet (hubs, coax) had to detect and recover from. A broadcast domain is the set of devices that receive a copy of a broadcast frame — a Layer 2 delivery boundary, not a physical-collision boundary at all. A modern switch happens to eliminate the first kind of domain almost entirely, port by port. It does nothing whatsoever to shrink the second — and that gap is where a lot of real-world "why is this switched network still slow" problems come from. This explainer builds directly on the companion piece on switching vs. routing — that one covers what switches and routers do with a frame; this one covers the scope boundaries their forwarding behavior creates.