How to clean up substreams in continuous Akka streams

Given I have a very long running stream of events flowing through something as show below. When a long time has passed there will be lots of sub streams created that is no longer needed.

Is there a way to clean up a specific substream at a given time, for example the substream created by id 3 should be cleaned and the state in the scan method lost at 13Pm (expires property of Wid)?

case class Wid(id: Int, v: String, expires: LocalDateTime)
test("Substream with scan") {
  val (pub, sub) = TestSource.probe[Wid]
    .groupBy(Int.MaxValue, _.id)
    .scan("")((a: String, b: Wid) => a + b.v)
    .mergeSubstreams
    .toMat(TestSink.probe[String])(Keep.both)
    .run()
}