Matrix - Reset Cumulation

I've been restling with this for a few days now and cant seem to get it right.

I am using a dax statment to provide a cummulation figure in a matrix that works.

The next step was to  - Check to see
if the Total Marks = Present then continue 

CALCULATE(SUM('Attendance (Table)'[Present]),
FILTER(
ALL('Academic Year (Table)'),
'Academic Year (Table)'[Week Ending]<= MAX('Academic Year (Table)'[Week Ending])))

Then to check if they had reached the threshold 

if the Cumulation reached 21 then reset the Cumulation to 0

Any help greatly appreciated.