This command refreshes the segments and memory contents in IDA. It is available only during a debugging session. NOTE: this command is currently hidden from the user interface because IDA does synchronize with the process memory automatically.
Please note that IDA itself tries to keep the program segments in sync with the debugged process. However, in order to accelerate the debugger, the synchronization is done only at major events, for example when dynamic library gets loaded or unloaded or a thread is created or deleted. If the memory configuration is changed because of a simple system call (think of VirtualAlloc), IDA might miss it. Use the "refresh memory" command in these cases.
Note2: when IDA detects a discrepancy in the segments, it will automatically synchronize with the process.
See also Debugger submenu.