In the User and Reference Guide for the Intel C++ Compiler 15.0, the description of the AVX2 intrinsics _mm256_cmpeq_epi8/16/32/64 states:
If a pair of data elements is equal, the corresponding data element in the destination vector is set to 1.
However, the description of the corresponding AVX2 instructions in the Intel 64 and IA-32 Architectures Software Developer's Manual states:
If a pair of data elements is equal, the corresponding data element in the destination operand is set to all 1s
The latter description appears to be correct.