This sounds alot like my mare.  I also believe it's some sort of 
fungus/infection.  Special has what I assume is a recurring case of mud 
fever. I think that it is because the former owners kept her in 
very deep mud, alot of the time, and never rinsed her legs off.  When I 
first bought her (during the muddy season), after cleaning her up I 
noticed caked "muddy scabs", that I couldn't remove.  (She also has 
white socks, and it seems to be worse where they are)  If I rubbed gently 
some would come off.  If I picked off ones that weren't ready they would 
bleed.  Always, when they came off the hair underneath would be gone.  It 
took me WEEKS to get ride of all of them!
  
Now when I bring her in from a muddy pasture I hose off her legs, and rub 
them down.  One time last December there was a family problem, so I quickly 
brought her in from pasture, and didn't hose off her legs.  The next 
morning when I went out her lower legs were swollen to the thickness of her 
knees!  I have come to the conclusion (feel free to offer feedback) that 
she *CANNOT* be left in deep mud, and I must *ALWAYS* hose off her legs 
when I bring her in.
>     Most people I have talked to who feel they have sucessfully handled
> scratches use some sort of a drying agent.
I use Absorbine Liniment.  It seems to really help.  I just rub her legs 
with it after I hose them off.
	><><><Here in Oregon the Muddy Season has Begun!!<><><>
<<Opinions are like belly buttons>>  	      The Purple Demon --,'-@   
<<Everybody's got one.....       >>	   ..............................