I think that here "dénonciation" refers to formal notice of the writ given to the party (this is usually a third party, although from what you say, it seems this is not the case here) and does not have anything to do with refuting it. When "dénonciation" is used in relation to process (the writ in this case) rather than substance (the actual arguments) it generally has the meaning of "notice" in French.
For an example, please see http://www.textes.justice.gouv.fr/art_pix/104-DACS-a.pdf (p. 8). The relevant decree, which you can find on the Légifrance site (see reference below) is "Décret n° 2006-936 du 27 juillet 2006 relatif aux procédures de saisie immobilière et de distribution du prix d'un immeuble" (see Articles 40-42) Of course, this is about attachment of property, but the principle remains the same in other cases.
For an example in English see http://www.irs.gov/pub/irs-tege/epche12c03.pdf (p. 12)