Is it possible to use the exists validation rule when using embedded models?

Let's say I have my Foo model which EmbedsMany Bar models. In my DB I have something like this:

{
 "_id": "...",
 "foo_attr": "val",
 "bars": [
 {
 "_id": "...",
 "bar_attr": "val"
 },
 // More bars...
 ]
}

Is there a way I could use Laravel's exists rule for validating a bar id? Maybe something like this?

'bar_id' => 'exists:foos.bars,_id'