Hello Benoit,
I believe the total transactions value displayed in ' Virtual Services: Current Status' is stored under the $lisatmp_dir.
When you delete the entire folder it will reset that current txn count.
In case you would like to view the total transactions for the VSE you can go under Reporting/ Virtual Service Metrics and you will be able to generate charts for 'VSE Lifetime Total Transactions' and 'Transaction Daily Counts'.
Hope it helps.
Heloisa