The problem with your calculation is that SUM([Sum]) will be evaluated for the whole pivot table, so get a table grand-total.
This being said, you cannot create a measure that says "Total of the column". You can, however, calculate the total for all selected products, or for the currently selected year, ...
The following measure calculates the total of "Sum" for all selected products.
Total - Selected Products :=
CALCULATE( SUM([Sum] ), ALLSELECTED(YourTableName[Name] ))
The following measure calculates the total of "Sum" does some sort of "ALLSELECTED EXCEPT Year" calculation (grand total for the current year):
Grand Total - Year :=
CALCULATE( SUM([Sum] ), ALLSELECTED(), VALUES(YourTableName[Year]))
For the given layout, both calculations will return the same results, but if you had another attribute in your table like "Country", they would give different results.
Take a look at both measures, to see which one is best suited.