What is the test for obtaining injunctive relief for an Eighth Amendment violation?

In order to obtain injunctive relief for an Eighth Amendment violation, plaintiffs must present evidence sufficient to give rise to an inference that defendants are "knowingly and unreasonably disregarding an objectively intolerable risk of harm" and that defendants will continue to disregard the risk into the future. Farmer v. Brennan, 511 U.S. at 846. To avoid entry of an injunction, defendants may prove either that they were unaware of the risk of harm or that they have responded reasonably to it. Id.