Garlic is very cold hardy, but your top growth may be damaged and have to regrow itself in the spring.

Generally garlic is planted in the fall (Oct/Nov) to establish good root growth before the ground freezes while minimizing top growth. If the tops are large and exposed they may be damaged but the cold, but should regrow in March. I suggest you mulch the top of the soil and put some insulation around the sides of the pot since potted plant get colder than in ground plants.

TomNJ

Similarly, I moved into a home last month that came with a fenced veggie garden (yippee!) It looks like the previous tenant planted garlic and onions late in the year though. Frost has killed off everything but the raspberries, but the garlic and onion leaves are still quite green and upright.

Can I divide the garlic cloves now and replant them for next summer's harvest?

If the previous tenant planted them recently, like August or later, I would leave them alone. If the leaves are green they are not ready for pulling.

TomNJ