The easiest thing to do is to get SQL to do the heavy lifting for you and prepare the data in a way that is most convenient for reporting. So what we want to do is get all the data that relates to the current week's business days - that is, anything from the Monday of this week to the Friday of this week:
SELECT PersonId, SomeDate
FROM MyTable
WHERE SomeDate >= DateAdd('d', 0 - (WeekDay(Today())-2), Today()) // Monday
AND SomeDate <= DateAdd('d', 0 - (WeekDay(Today())-6), Today()) // Friday
Then you just feed this into your matrix, grouping on the person and the date and you're good to go.