This one worked for me:

def list = [1,2,3,4]
for(item in list){
    println item
}

Source: Wikia.

You can use the below groovy code for maps with for-each loop.

def map=[key1:'value1', key2:'value2']

for (item in map) {
  log.info item.value // this will print value1 value2
  log.info item       // this will print key1=value1 key2=value2
}

Your code works fine.

def list = [["c":"d"], ["e":"f"], ["g":"h"]]
Map tmpHM = [1:"second (e:f)", 0:"first (c:d)", 2:"third (g:h)"]

for (objKey in tmpHM.keySet()) {   
    HashMap objHM = (HashMap) list.get(objKey);
    print("objHM: ${objHM}  , ")
}

prints objHM: [e:f] , objHM: [c:d] , objHM: [g:h] ,

See

Then click "edit in console", "execute script"