per default only "backviews"-are gonna cached.
If your product page is the endpoint of your navigation structure --> it is not cached:
Home --> product list --> product Detail (you only can go back to list and to another detail page)
you can activate forward-caching via the $ionicConfigProvider
http://ionicframework.com/docs/api/provider/$ionicConfigProvider/
$ionicConfigProvider.views.forwardCache(true);