Datagrid remove all?

Hi,
I’ve been trying to remove all data from a datagrid to avoid having the old values plus the new values all the time but it doesn’t seem to work
I feed a datagrid from a xml and each time I try to load a new one, it simply adds to the previous.
I tried:
myDatagrid.removeAllColumns();
myDatagrid.dataProvider.removeAll();
Before adding new data but I still have the old values PLUS the new ones.
Any idea on what I’m missing?
Thanks a lot:)