Himalayan Blackberry and Evergreen Blackberry are European species that were brought into Washington State as a fruit crop. They are now one of the most invasive species in this part of the state and in some spots cover more area than all of the other invasive species combined.
If you are curious about goats in general, or using goats to clear blackberries or other brush, Rent-a-Ruminant has a cute website with some good information. Rent-a-Ruminant is a company based in Vashon Island, Washington that rents out a goat herd to clear brush. Really quite fascinating - the woman who started it was a paramedic and worked in the burn unit at a Seattle Hospital. She decided she needed a break from that life and started with 10 goats and eventually grew her herd to over a hundred. She rents her goats out to people who want to clear brush off of land. The goats are confined inside an electrified fence while they work the land and can clear blackberries, ivy and other invasive species from about 1/4 acre in 3 days.
Goats, like cows, goats, sheep and deer, are ruminants with multi-compartmented stomachs. They regurgitate their food (cud) and chew it again, which helps explain how they can eat woody things like blackberry canes and the bark off trees. Unlike sheep who graze and will eat grass to the ground, goats are browsers who like to munch on things higher up. When goats are used to clear brush, any trees that the owner wants to keep have to be fenced off.
There's a 3 part interview with Tammy Dunakin, the owner of Rent-a-Ruminant, on YouTube where she talks about her goats. She has Snowflake her "ambassagoat" with her. She says the goats favorite food is blackberry bushes, but they won't eat the big blackberry canes. From the looks of the before and after photos they eat enough of the blackberry bramble to make it a lot easier to clean up what they leave, and if the goats are brought back to the same area for a few seasons they will get rid of the blackberry brambles. In the interview she says she has more business than she can handle and would like to involve people in franchise rent a goat operations.