Ivar,
The odour has probably permeated every absorbant surface, including walls.
After cleaning any soft furnishings, using an appropriate odour neutraliser such as the one Steve sugested.
Next open all windows and force-ventilate with turbo blowers, then close up and thermal fog either with same product (check with Nick for suitability) or with something like Prochem A222.
Flat must then be closed for at least 12 hours.
The odour of curry is not only pervasive, it is very persistant. Customer should be pre-warned that a second fogging may be required and even then some odour may remain.
John.