Is there a way to query if one chunk has already been "initialized" (written to)?

If I have a (very) sparse dataset and I always write exactly whole chunks,
is there a way for me to iterate over all the written chunks explicitly?
Using a fill value is just not an option in my case.

MfG / Regards,
Sebastien Diot

Grossblittersdorferstrasse 257-259
66119 Saarbruecken
Germany
Tel.: +49 (681) 8808-0
Fax.: +49 (681) 8808-300
E-Mail.: s.diot@eurodata.de

···

-----------------------------------------------------
EURO DATA GmbH & Co. KG
Datenverarbeitungsdienst
HR A 6448 Amtsgericht Saarbrücken
Komplementär: A. Reiß & Sohn GmbH
HR B 4965 Amtsgericht Saarbrücken
Geschäftsführer: Dipl.-Kfm. Karl-Heinz Siebenpfeiffer
-----------------------------------------------------