Hi,

I have a custom field - Prod_Value_Currency_Field__c on Products standard object and 2 formula fields each on OppProducts (OLI_Value__c) and Assets(Asset_Value__c) which takes the value of the related Product's Prod_Value_Currency_Field__c . 
I need two roll up summary fields at the Opportunity and Account objects level. So, I wrote two workflow rules, each on OppProds and Assets to copy the value of OLI_Value__c and  Asset_Value__c so that I can do a roll up summary on the Opp (SUM(COPY_of_OLI_Value__c )) and its Account(SUM(COPY_of_Asset_Value__c )).
This will work if there are no changes to the "Prod_Value_Currency_Field__c " value.
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Now the "Prod_Value_Currency_Field__c" changes often (gets updated via dataloader) on Products , my formula fields will get updated but the copy fields will not. I am trying to find a way to track the changes in "Prod_Value_Currency_Field__c"  to update the copy fields on OLIs and Assets.   
(1. I cannot track changes of formula fields in WFR as formula fields are not stored in database and also 
2. cannot track changes of cross object fields in WFR (cannot track changes in Prod_Value_Currency_Field__c at Product level in OppProductsWFR and Assets WFR ))


Can anyone suggest a way/give clue to get around this problem here?  
Thanks for your time.