If you perform a Query or Get on the data that is populating the Grid that should reset it to the order you originally had it before users started sorting the data. I would try grabbing the initial data set again upon a button click, or something that can fire off the Query/Get service that pulls in the data, and have it repopulate the Grid.
Thank you for your suggestion. Unfortunately, refreshing the data tied to a grid does not remove the sorting on a grid that comes from clicking on a grid column header. I've checked with PTC and there is not currently a way to override the manual sort via a grid column header, other than reloading the webpage. I am trying to get it submitted as a change order for a future release of ThingWorx.