what you are actually referring to is people being able to buy and sell positions at different 'net MC' values accross the two market.
This isn't an exchange of stock between the two exchanges, it is just using the difference in valuation between the Australian MC and the American MC (given that you take into account the ratio of shares compared to the governed total MC) to find trade opportunities of switching from US stock to Australian stock.
You can do this yourself if you have an international share account and an australian one... and the necessary time required to find the valuation differences and which market is correcting to the other (although very rarely does australia lead the US, so probably not that difficult)..
