Is it a concrete foundation or what? No type of dust can be called good for you, but some are worse than others. Wet-cleaning is probably safer than vacuum, but if you have a lot of micro-filter bags, the dust will be contained, more or less. Contaminants on the dust (like hanta-virus) could well be blown airborne though..
A bleach and water spray is not a bad plan if you want to kill micro organisms. THat won't stop an intrinsically toxic dust from being toxic though, and if your dust is (let's take a worst case scenario) from tailings at the mine or something, then you don't want to handle it yourself.
What colour is the dirt around your house?