My example code was correct and the issue was something else in my actual code. Still, I know it was difficult to find examples of this so I'm answering it in case someone else is looking.
<div ng-repeat="f in foos">
<div>
<div ng-repeat="b in foos.bars">
<a ng-click="addSomething($parent.$index)">Add Something</a>
</div>
</div>
</div>