Many moon ago there were reports that LH at IAD allowed Domestic F, but as the *A site states this is a lounge decision and could change
Domestic First Class Customers
Some member airlines offer lounge access at the airport where your flight departs, if you are travelling in Domestic First Class. Restrictions apply for Domestic First Class passengers travelling with United Airlines in the United States, where Domestic First Class customers do not have access to United’s Club lounges.
You will need to show your boarding pass in Domestic First Class for a Star Alliance member airline operated flight. You are entitled to bring one guest travelling on any Star Alliance flight departing from the same airport on the same day.