In order to zero out data points you can do it either:
- from Cube Viewer
select all the cells with the pointer
right click: Data Spread->Clear...
or
select the top left corner cell of the portion to zero out
right click: Data Spread->Repeat
set value box to 0 and tick boxes Extend "right" and "down"

- from a TI process
in the Prolog tab:
ViewZeroOut('Cube','View');

setup the 'View' to zero out then run that process