Common dogwoods will survive in zone 4. They grow in all zones of the US except desert areas. I wasn't meaning my comment to mean specifically dogwoods anyway, I was just stating that one person's idea of full sun, may not be another person's circumstances.
But speaking specifically about the dogwood, I'm venturing a guess that a dogwood needs afternoon shade in zone 7 to be really happy. But again if it were supplementally watered, maybe it would do okay. If you planted that same tree in zone 4 with afternoon shade it would probably live but not bloom. I am in zone 6 and have a dogwood in full shade, it grows fine but has never bloomed for me. My dogwood in full sun do fine for me.