I'd recommend taking the following steps to resolve your scanning issue: Are both Macs running OS X 10.10 (Yosemite)? Sometimes Yosemite will automatically install the printer using the AirPrint driver (which has limited capabilities) so it may be as simple as your printer being added with the wrong driver.
If you are able to scan without issue from one Mac, then we know that the issue lies on the Mac where you are unable to scan.
I understand you are having an issue scanning to one of your Mac 10.10 computers from your HP Officejet 6700 Premium e-All-in-One printer.
I hope you have a pleasant experience here.