The xclip manpages (
man xclip) say this:
specify which X selection to use, options are "primary" to use XA_PRIMARY
(default), "secondary" for XA_SECONDARY or "clipboard" for XA_CLIPBOARD
So you can specify the location:
echo !! | xclip -selection <selection>
<selection> is one of
Description of these from the ArchWiki: Clipboard
Of the three selections, users should only be concerned with PRIMARY and CLIPBOARD. SECONDARY is only used inconsistently and was intended as an alternate to PRIMARY. Different applications may treat PRIMARY and CLIPBOARD differently; however, there is a degree of consensus that CLIPBOARD should be used for Windows-style clipboard operations, while PRIMARY should exist as a "quick" option, where text can be selected using the mouse or keyboard, then pasted using the middle mouse button (or some emulation of it). This can cause confusion and, in some cases, inconsistent or undesirable results from rogue applications.
That means it depends on your environment. It may have inconsistencies, if the applications use different selections. Though if you use a desktop enivornment like Gnome it should work fine.
Also as mentioned by Kartik, you can copy-paste in most terminals with Ctrl+Shift+C/V.
Most applications in linux also support selection of text with the mouse to store something in the clipboard.
To get the content of from the clipboard use the -o flag:
If you use it often you can create aliases for those commands in you .bashrc:
alias cbcopy='xclip -selection clipboard'
alias cbpaste='xclip -selection clipboard -o'