That appears to be the meaning. Soulte is an old word presumably related to modern-day solde in the sense of "balance" or "payment to make up the full amount". If you retourne money to someone, you refund that person.

I'll leave you to find a suitably archaic legalistic expression or to put it in plain English as you see fit!

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Note added at 21 mins (2010-01-26 00:41:07 GMT)
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In the case below it's an exchange that has taken place:

It means that parties to a contract have exchanged assets and no one has paid anything in addition ( which might have happened if the assets were of different value, in which case whoever gets the lesser asset also gets financial contribution towards fair exchange :this financial contribution is called soulte)
http://forum.wordreference.com/showthread.php?t=772813

Off the top of my head I don't know what abandonnement means or whether any financial transaction took place in the first instance ...

Abandonnement, Cession de biens ou de droits, volontaire ou forcée, qu'un débiteur fait à ses créanciers. Ab intestat, qui n'a pas fait de testament. ...
collections.civilisations.ca/gene/c360_21f.html

OK, so it looks as if there was no financial transaction, the deal amounting to an "exchange" as described above, i.e. Party A owes money to Party B and gives Party B property in exchange for cancellation of the debt, without any fine-tuning of the deal to account for any differences in the value of the property as compared to the amount of the debt.