tableview1.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
    if (newSelection != null) {
        tableview2.getSelectionModel().clearSelection();
    }
});

tableview2.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
    if (newSelection != null) {
        tableview1.getSelectionModel().clearSelection();
    }
});