There's 2 ways I can think of to achieve this, the first one is Josh Milligan's default values technique.
Another method I've had success with is to pass it a rubbish value like 1:1 over a parameter filter, and Tableau throws an error and shows you everything.
Step 1 - create State Parameter, note the value All with the Display As title of 'Australia'
Step 2 - create calculated field - note the value 1=1 for Australia
Step 3 - build your viz and expose parameter control
What occurs is when each state and territory is selected, the calculated field will select it and highlight it. When Australia is selected, Tableau defaults to 'nothing is selected' mode, and displays everything.
For someone who will land on this post, We recently upgraded the tableau server version to 2019.3.1 and see that the the JS API has a new method introduced called 'getIsAllSelected', which returns a boolean value based on if All is set on the filter or not.
At the time of writing this the official documentation does not have a reference to it, but I am sure it would be added soon.