What Scale Could Be Used For This Progression? Em C D B

I'm very fond of playing the following progression: E minor, C, D, B. It has a little bit of a middle Eastern/exotic feel. I'm curious what scale I could use to solo over it? What key is this progression in? And what would be the number system for these chords? I very much appreciate any help, I'm new to music theory.

PS: a good example of this progression is Desert Rose by Sting (in a different key though).

E minor probably. It has a both a natural and raised seventh, which is pretty normal.

i - VI - VII - V

I would use the harmonic form of E minor. Which is E-F#-G-A-B-C-D#-E. The C goes with the C chord, and the D# goes with the B chord which could easily be B7.

i don't think of scales so much, but rather the harmony of the song (following each chord). even this is replaceable and extendable. so when i'm on the e minor chord, i know i could add a G7 in the last part to prepare the upcoming C chord for example.  it is usefull to realise i'm in e minor tonality, and the roles of the other chords, but thinking of a scale to play serves no good imo.

I think Ken's got it closest, and would depend somewhat on how quickly things were going by how much I'd lay on anything really definitive. I'd tend towards E Aeolian (Natural Minor, 6th mode of GMaj) until the B chord (clearly is a dominant - likely a B7(b9) where a flip to the harmonic minor will get you that D# leading tone...

Even the D chord works nicely as a D7(b9) where the Eb (D#) really helps define the harmonic movement from the Emin to the B dominant...

i don't think of scales so much, ... thinking of a scale to play serves no good imo.

As an improvisor, I find it much more interesting to think in linear terms. If you dwell only on the chord your ON, you'll never find a good way to get to the chord you WILL be on... or the chord 8 bars from now. ;)  

I need to play melodies. If I just outline changes, then I'll get real bored, real fast.