Your spec is pretty minimal, but here's one way to achieve your goal:

#! perl -slw
use strict;
use Data::Dump qw[ pp ];

my $text = do{ local $/; <DATA>; };

my( $n, @scopes ) = 1;

1 while $text =~ s[
    ( \{ [^{}]+ \} )
]{
    push @scopes, $1;
    '_' . $n++ . '_';
}gex;

s[scope (\d+) text][processed text $1]g for @scopes;

$text =~ s[_${ \( $_+1 ) }_]{ $scopes[ $_ ] }eg for reverse 0 .. $#sco
+pes;

print $text;

__DATA__
text text {scope 4 text {scope 2 text {scope 1 text} scope 2 text} sco
+pe 4 text {scope 3 text} scope 4 text } text text
[download]

Output:

C:\test>1139932
text text {processed text 4 {processed text 2 {processed text 1} proce
+ssed text 2} processed text 4 {processed text 3} processed text 4 } t
+ext text
[download]