According to 13.7.6 [temp.spec.partial] paragraph 6,

A class template partial specialization may be declared or redeclared in any namespace scope in which its definition may be defined (13.7.2 [temp.class] and 13.7.3 [temp.mem]).

However, there is nothing in those referenced sections specifying where the definition may appear. Should this have referred to the definition of the primary template?

Also, the cross-reference to 13.7.2 [temp.class] is suspect; the actual rules for where non-member class templates may be defined are found in _N4868_.9.8.2.3 [namespace.memdef] paragraphs 1-2, 9.3.4 [dcl.meaning] paragraph 1, and 9.9.2 [namespace.def] paragraph 8.

(Apropos of 9.9.2 [namespace.def], the description in paragraph 8 mentions explicit instantiation and explicit specialization, but presumably inadvertently omits partial specializations.)