The FLIX utility under the link
http://www.ledas.ac.uk/flix/flix.html
can be used to check, for a given sky location, whether
XMM-Newton has observed that region of the sky and if so, determine XMM-Newton
upper limits, X-ray fluxes, and create image cut-outs.
Alternatively, the XMM-Newton Upper Limit Server can be used:
http://xmm.esac.esa.int/external/xmm_products/slew_survey/upper_limit/uls.shtml.