Exercises 4.11 and 4.12 and Corollary 6.6 of David Eisenbud, Commutative Algebra with a view towards Algebraic Geometry, GTM 150, Springer-Verlag, 1995. Also, Milne 1980 Milne, James (1980). Étale cohomology. Princeton Univ. Press. ISBN0-691-08238-3.