作ったブランチ（sub-branch）を用いて、masterブランチを完全に書き換える。
$ git checkout sub-branch
$ git merge -s ours master
$ git checkout master
$ git merge sub-branch
$ git push origin master
-s ours = --strategy=ours
Use the given merge strategy; can be supplied more than once to specify them in the order they should be tried.
If there is no -s option, a built-in list of strategies is used instead (git merge-recursive when merging a single head, git merge-octopus otherwise).
以上です。
参照
git-merge