I was having the same trouble with breaking my broody girl this past week. And caging her was not working. So I filled up a large tub of cold water and soaked her in it for 5 full mins! She was good for about 5 hours and I caught her back in the nest box growling at me and guarding her fake egg. So she got another "broody soak". And this time it worked!! She has been broody free for one and a half days. She is back to eating again, which she had stopped doing and is now hanging out with the girls instead of dreaming of baby chicks!
Edit to add: During broodiness, the hens temperature rises and by soaking the broody, lowers her temp and her hormones tell her she is not warm enough to brood chicks.
Good luck!