It sounds like you may be using data blending to combine the data from the two data sources into one view. Typically I recommend doing a table join as data blending has many limits. If the two data sources are in different databases, then a cross-database join will work. For directions, please see the following entry of the online Product Help guide Join Your Data - Tableau
If you stay with data blending and using TOTAL(), then the way the total is computed can be changed. The simplest way is to right-click the field in the view and select Compute using > Table (down). I really like how this entry of the online Product Help guide explains more advanced table calculation options: Transform Values with Table Calculations - Tableau
Hope this answers your question!