Answer: You'll want to check the stems of your plant for life before cutting it back. Start at a convenient spot (something you can easily reach) and scrape the bark off the stem with your fingernail. If you see green tissue beneath the bark, that stem is still alive at that point and new leaves will emerge when the weather warms. If the area is brown rather than green, go further down on the stem and scrape the bark. Keep working your way down the stems until you find live material. That's the point where you'll want to cut the plant back. Bougainvillea is such as vigorous grower that even if you end up cutting most of the plant back it should recover and replace the lost growth this spring and summer.
Best wishes with your bougainvillea!
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